Numerous studies have been performed consisting in modifying the nature of diene polymers and copolymers through functionalizing agents.
A functional ESBR with glycidyl methacrylate (GMA) is described in U.S. patent application No. 2011/0098404 A1. According to the inventors “Copolymer of styrene-butadiene obtained by emulsion polymerization presents poor compatibility with silica”. In this patent application, inventors reported the development of a functional styrene-butadiene copolymer by emulsion polymerization with improved silica compatibility by polymerizing styrene-butadiene copolymer using an epoxy acrylate monomer and then performing ring-opening of the epoxy group with 20% aqueous solution of sulfuric acid (H2SO4) or potassium hydroxide (KOH). This functional ESBR was used in compound preparation with silica, which is said to have superior tensile property, wear resistance and wet stopping (tan delta at 0° C.). This patent application claims a functional styrene-butadiene copolymer with monomers having functional groups like amine, hydroxyl, alkoxy, sulfonate, carboxylate, phosphonate, halogen, thiol and azide; a silica composite for tire; hoses or belts and a method for preparing said functional styrene-butadiene copolymer which comprises performing a ring-opening the epoxy.
A rubber that produces a vulcanizate with low rolling resistance, good wet skid and improved wear resistance for automobile tire treads is described in U.S. Pat. No. 6,699,935 B2. The inventors used polymerizable unsaturated groups such as divinylbenzene, carboxylic, hydroxyl and/or epoxy groups. In this Patent it is reported that rolling resistance can be reduced by lowering hysteresis loss of the vulcanized rubber (low heat release). Tires treads which use inorganic fillers like silica show low rolling resistance and excellent driving stability (wet skid). On the other hand, they exhibit poor tensile strength and wear resistance. The reason is believed to be the poor interaction polymer-silica compared to carbon black. In order to overcome this problem, it has been proposed to obtain a polymer with functional group that can be able to interact with inorganic fillers (silica). However, due to strong interaction that these groups promote with polymer, it creates problems of filler dispersion, heat release during processing and poor processability. Researchers' challenge is to find the appropriate amount of functional monomer incorporated in the polymer that can combine properties with processability. U.S. Pat. No. 6,699,935 B2 claims a rubber composition having polymerizable monomer with functional group comprising carboxylic, amino, hydroxyl, epoxy and alkoxysilyl groups. Examples of carboxylic groups: (meth)acrylic acid, maleic acid, itaconic acid and the like. Examples of amino groups: dimethylaminomethyl(meth)acrylate, diethylaminomethyl(meth)acrylate, N,N-diethyl-p-aminostyrene, 2-vinylpyridine and the like. Examples of hydroxy groups: 2-hydroxyethyl(meth)acrylate, 3-hydroxypropyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate, p-hydroxystyrene and the like. Examples of epoxy groups: (meth)allyglycidylether, glycidyl(meth)acrylate and 3,4-oxycyclohexyl(meth)acrylate. Examples of alkoxysilane groups: (meth)acryloxymethyltrimethoxy silane, (meth)acryloxymethyldimethoxy silane, gamma-methacryloxypropyl tripropoxysilane and the like. It is mentioned in this invention that is possible to have a combination of two or more functional monomers having carboxylic, hydroxyl or epoxy groups. For example, it is possible to have a combination of a carboxylic group monomer and a hydroxyl group monomer. U.S. Pat. No. 6,699,935 also claims a tire composition with mentioned functional polymers.
U.S. Pat. No. 4,574,140 discloses a process for obtaining a synthetic elastomer copolymer with improved “green strength”, defined in the invention as “a property of a polymer or elastomer common in natural rubber, which contributes to the proper building conditions, generally measured by stress-strain measurements”. The process for obtaining such polymers was emulsion polymerization by free radicals utilizing conventional practices and procedures, such as temperature, pressure and time through free radical initiators. Emulsion polymerization was performed at pH from 10 to 11, although authors state that it should not be limiting. These polymers with pendant hydroxyl groups can be blended in Banbury with another copolymers like natural rubber, cis and trans polybutadiene, both cis and trans polyisoprene, polypropylene, a copolymer of butadiene and styrene, a copolymer of alpha-methylstyrene and butadiene, high cis-1,4-polyisoprene and high cis-1,4-polybutadiene. The blending can be performed by the form of latex and can be mixed with a latex of an elastomer such as polybutadiene, a copolymer of styrene and butadiene and nitrile latex. The terpolymer can be partially crosslinked by the addition of crosslinking agents such as diisocyanates. Examples of monomers used to functionalize the polymer are: hydroxy propyl methacrylate, hydroxy ethyl methacrylate, hydroxy ethyl acrylate and hydroxy propyl acrylate. Example 3 of this invention shows terpolymers of styrene-butadiene-HEMA (hydroxyl ethyl methacrylate) and styrene-butadiene with glycidyl methacrylate (GMA). The latexes were stripped, coagulated and compounded using carbon black in the recipe. According to the inventors, HEMA terpolymer compounds exhibited better resilience than compounds of GMA terpolymer. This patent claims a process for forming a synthetic elastomer copolymer having improved green strength comprising reacting at least one type of a synthetic elastomer forming monomer with a hydroxyl group wherein said hydroxyl containing monomer is selected from the group consisting of hydroxyethyl methacrylate, hydroxy propyl methacrylate, hydroxyethyl acrylate and hydroxy propyl acrylate.
U.S. Pat. No. 6,653,404 B2 describes a process for obtaining a rubber with functional monomers like diethylaminomethyl(meth)acrylate, hydroxypropyl(meth)acrylate, o,m,p-hydroxystyrene, glycidyl(metha)crylate, alkoxysilyl groups (meth)acryloxymethyltrimethoxy silane and the like. According to this invention, a rubber composition presents satisfactory processability with silica. Rubber composition with silica and carbon black is said to have excellent tensile strength and wearing resistance.
U.S. Pat. No. 7,108,033 B2 discloses an invention for obtaining polymers that exhibits low hysteresis and good compatibility with fillers, like carbon black and silica. Functional monomers are derived from one or more conjugated diolefin monomers with a leaving group, such as halogen (chlorine, bromine and iodine). According to the inventors, the polymerization system can be carried out by bulk polymerization, vapor phase polymerization, solution polymerization, suspension and emulsion polymerization, but emulsion polymerization is the commercially preferred one. Examples of these monomers are: 4-vinylbenzyl chloride, 4-vinylbenzyl bromide, 4-vinylbenzyl thiocyanate. Functional polymers were compounded using in the recipe carbon black and silica. Dynamic tests shown that compounds from functional polymer with 4-vinylbenzyl chloride exhibited hysteresis reduction, what is an indication of improvement in polymer-filler interaction, mainly with silica. This patent claims a tire which is comprised of a generally toroidal-shaped carcass with an outer circumferential tread and a rubbery composition with the mentioned functional monomers.
U.S. Pat. No. 6,455,655 B1, U.S. Pat. No. 6,512,053 B1 and U.S. Pat. No. 6,716,925 B2 disclose an emulsion styrene-butadiene rubber (ESBR) with properties like rolling resistance and tread wear similar to those of solution SBR but with improved traction characteristics when employed in formulations for tire tread. This rubber is characterized by the incorporation of a hydroxy alkyl acrylate monomer in the polymer chain, more specifically hydroxypropylmethacrylate. In U.S. Pat. No. 6,455,655 B1 and U.S. Pat. No. 6,512,053 B1, lattices with low and high molecular weight are produced separately. In U.S. Pat. No. 6,455,655 B1, hydroxypropylmethacrylate monomer is preferably incorporated during polymerization for attaining the high molecular weight rubber and its level ranges from about 3 weight percent to about 5 weight percent. The polymerization temperature ranges from 7° C. to 13° C. Latex with high molecular weight and with low molecular weight are blended and coagulated with brine and dilute sulfuric acid or aluminum sulfate. Crumbs were washed and dried. In order to obtain desired characteristics, emulsion SBR of this invention can be blended with other polymers and co-cured. Examples of such polymers include natural rubber, high cis-1,4-polybutadiene, high vinyl polybutadiene, medium vinyl polybutadiene, high trans-1,4-polybutadiene, solution styrene-butadiene, styrene-isoprene-butadiene, styrene-isoprene, isoprene-butadiene and 3,4-polyisoprene. U.S. Pat. No. 6,455,655 B1 claims a styrene-butadiene rubber composition wherein the hydroxy alkyl acrylate, specifically hydroxypropylmethacrylate, is bound in the polymer at a level that ranges from about 3 percent to about 5 percent and a tire having a tread that is comprised of the styrene-butadiene rubber composition specified in the invention wherein the filler is selected from the group consisting of carbon black and silica.
It is well known in the state of the art that ESBR polymers exhibit their better performance in terms of rolling resistance, tear resistance and wear resistance when produced with high molecular weight. However, those high molecular weight polymers are difficult to process in blending equipments generally used in the rubber compounding industry.
To overcome this technical problem it is a general practice in the synthetic rubber production plants to incorporate extension oils to the high molecular weight polymers in order to improve their processability in rubber compounding plants.
The state of art documents described above and general technical literature do not comment the role of extension oils in the properties or processability of polar modified ESBR. They are mainly centered on polar functionalization agents introduced in polymer chain without taking care of the chemical nature of the extension oil to be used.
Extension oils for ESBR are key components for dictating their compatibility, processability and properties. For this reason, it is very important that extension oils are chemically compatible to the polymer backbone and filler used for compounding.
Extension oils currently used in ESBR production are from fossil origin and based on non-polar fractions of petroleum hydrocarbons having a certain composition of aromatic, naphthenic and paraffinic compounds.
Aromatic compounds are more compatible to ESBR polymer chains than naphthenic and paraffinic compounds in this sequence. Regarding carbon black compatibility the same sequence is followed.
Nevertheless, oil fractions are richer in paraffinic compounds and for this reason it is very important to control the level of aromatic and naphthenic carbons keeping a minimum amount of such compounds in extension oil used to ESBR modification.
Additionally, highly aromatic oils were recently banned from rubber industry due to its high content of PAH (Poly Aromatic Hydrocarbons). They were replaced by TRAE (Treated Residual Aromatic Extract), TDAE (Treated Distillate Aromatic Extract), MES (Mild Extraction Solvate), HN (High Naphthenic) and other low PAH oils. However, those oils still present some amount of PAH compounds and all of them are derived from non renewable sources coming from different processes of crude petroleum distillation.